WASHINGTON (CNN) — One passenger has died after smoke filled the L’Enfant Plaza metro station in downtown Washington on Monday, a Washington Metropolitan Area Transit Authority spokeswoman told CNN. A total of 84 people were treated by local hospitals, according to emergency officials.

The station was temporarily closed after filling with smoke, while a disabled train was evacuated. D.C. Fire and EMS tweeted that one person was critically injured and six others were hurt in the incident after a train filled with smoke and its passengers were evacuated.

The National Transportation and Safety Board was investigating the incident and Metro Transit Police and fire department personnel were at the station examining the problem, WMATA said, but had not yet found the source of the problem as of Monday afternoon.

WMATA spokeswoman Morgan Dye told CNN Monday evening that while everyone in the station had been evacuated, they…